proton {<proton-statement>} end

<proton-statement> :==

  observed <atom-selection> [<atom-selection>] <real> [<real>]
  --{Set the observed proton shift or shifts for the protons in the
     selection(s) to the real value(s).}
  rcoil <atom-selection> <real>
  --{Set the random coil proton shift for all the protons in the
     selection to the real value(s).}
  anisotropy <atom-selection> <atom-selection> <atom-selection>
             co|cn [iscooh] sc|bb
  --{Select CA     CO    O  atoms (one in each selection).
     Say if its a CO or CN bond, if its part of a carboxyl group 
     (which are averaged together), and whether it is a backbone or 
     sidechain CO.}
  amides <atom-selection>
  --{Select all the backbone amide protons.}
  carbons <atom-selection>
  --{Select all the backbone carbonyl carbon atoms.}
  nitrogens <atom-selection>
  --{Select all the backbone nitrogen atoms.}
  oxygens <atom-selection>
  --{Select all the backbone oxygen atoms.}
  ringatoms phe|tyr|his|trp5|trp6|ade6|ade5|gua6|gua5|thy|cyt|ura
            <atom-selection> <atom-selection> <atom-selection>
            <atom-selection> <atom-selection>[<atom-selection>]
  --{Say how many atoms are in the ring, and select each one in turn.
     The last selection is only for six-member rings.}
  alphasandamides <atom-selection>
  --{Select both alpha and amide protons.}
  class=<classname>
  --{Starts a new class which applies to all assignment and force entries
     until another class entry is issued.}
  error <real>
  --{The error to be used by the current class in square well calculations.
     Default=0.3}
  forceconstant <real> [<real>]
  --{Force constant and Constantine force constant for all assignments
     in the current class. Default=0.1}
  potential square|harmonic|multiple
  --{Use shift errors or not.}
  print threshold <real> all|class=<classname> rmsd|normsd
  --{Print proton shift violations greater than the specified value
     (in ppm) for all classes or for the specified class and potentially 
     print the results to the rmsd array.}
  reset
  --{Erase the proton shift assignment table.}